Process for dehydrating watercontaining materials



y G A. SYKES EI'AL 2,318,027

PROCESS FOR DEHYDRATI ENG WATER-CONTAINING MATERIALS Filed March 6, 1,940

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PROCESS FOR DEHYDRATING WATER-CONTAINING MATERIALS Fil ed larch 6, 1940 4 Sheets-Sheet 5 INVENTORS GEORGE-H. SYKES G/VEg LOU/SE HNDREH ATTORNEY May 4, 1943. e. A. SYKES ETAL PROCESS FOR DEHYDRATING WATER-CONTAINING MATERIALS 4 Sheets-Sheet 4 91111411111117: h E :tiltllt! l m w u H a U m TEE O fi. sm A H. MAW WYQ B 55 u 65 N 6 H Patented May 4, 1943 UNITED STATES PATENT" OFFICE PROCESS FOR DEHYDRATING WATER,-

CONTAINING MATERIALS George A. Sykes and Agnes Louise Andrea, Sodus, N. Y.

Application March 6, 1940, Serial No. 322,504

- 4 Claims.. (01. 34-26) The present invention relates to a process'for dehydrating water-containing materials, and, more particularly, to a novel and improved process for dehydrating foodstuffs in such a manner as to retain their structure, integrity, .and vital principles, and to the products of such process.

As those skilled in the art know, the art of dehydrating is a. very old one, particularly the art of dehydrating or drying water-bearing materials. such as foodstuffs, which has been practiced to some extent at least throughout the entire history of the human race. A large number of methods and devices has been developed for drying moist and water-bearing materials. Due to the complexity of the problem, however, all of these prior methods provided an inferior product. The extreme complexity of the,problem will be readily understood if it is considered that during dehydration food products are greatly exposed to impregnation with bacteria, fungi, spores, and the like carried by the air which rendered the dehydrated products extremely dangerous to health and frequently caused early deterioration of the products. Similar difficulties were experienced with oxidation of the materials to be dehydrated prior and particularly during the process of dehydration. One of the .most grave diiliculties' encountered in dehydration was the so-ealled case-hardening" of the materials. In other words, the materials dried first at the surface giving a case hardening efiect. As the drying process continued, the internal water expanded due to the heat and, being unable to evaporate throughthe pores of the already hardened surface, rupture of the internal cell tructure occurred, causing checking and cracking. Thus, dehydration and drying as heretofore practiced was very destructive of the original cellular composition of the materials dried, and consequently an attempt to restore the materials to their original condition by adding water could not bring back the color and flavor of the fresh materials. To counteract this most serious diflicultyQit has beensuggested to introduce moisture, water vapor, etc. under various operating conditions, but these prior suggestions, although somewhat alleviating the difliculty, failed to provide -a full solution of the problem. Conventional dehydrated materials. particularly foodstuffs, had an unattractive appearance and even after restoring the original water content did .not even approach the appearance, flavor, and wholesomeness of the fresh materials. On the other hand, dehydrated materials had a number of unquestionable and important advantages. Thus, a dehydrated material has in most cases less than 15 or 20% of the weight of the original product, requires only a fraction of the space for storage and, if properly made, could be kept in storage for a number of years without deterioration. As a result, dehydration was practiced on a large scale since time immemorial, but due to the inferior quality of the dehydrated products, especially since the introduction of modern canning and freezing methodsv for the preservation of food, it has never attained the importance in the food economy of the human race, to which it isentitled.

From the foregoing considerations, it will be apparent that the art wasconfronted with a problem of extreme seriousness and of incalculable importance, for whichso far no wholly satisfactory solution has been found, especially insofar as commercial production on an industrial scale of acceptable products capable of restoration to their original condition has been concerned.

We have discovered a simple and completely condition by restoring their original content of water.

A further object of the invention is to provide a process for dehydrating water-containing organic materials during which the material is subjected to a plurality of periods of treatments during each of which the temperature, the humidity, the velocity of the gaseous medium, such as heated air, to which the material is exposed,- are critically controlled, to avoid'case-hardening, oxidation, and other difliculties experienced in prior processes.

Still another object of the inventiog is to provide a process for dehydrating foodstuffs of various character involving. rigid control of the humidity, temperature, including convective and conductive heat fiow, and radiant heat over and below the materials processed, gas velocity and other governing factors throughout the entire adapted to dehydrate large quantities of materials within an unprecedentedly short time and at a heretofore unattainable low cost on a practical and industrial scale.

The invention also contemplates a novel type of dehydrated product, particularly dehydrated foodstufis, having a fraction of the weight and of the space requirements of the fresh product, which can be stored indefinitely in ordinary storage space without refrigeration and which by the addition of water may be restored to substantially the original size, shape, and appearance of the fresh product and which as far as its taste, flavor, nutritiveness, and the presence of vital principles, such as vitamins, is concerned, is closely similar to the fresh material.

Other and further objects and advantages of the invention will become apparent from the following description taken in conjunction withthe accompanying drawings in which:

Fig. 1 illustrates a front elevational view of a Y preferred embodiment of a dehydrator for carrying the principles of the invention into practice;

Fig. 2 shows a plan view of the dehydrator illustrated in Fig. 1;

Fig. 3 depicts a vertical sectional view, having parts in elevation, of the dehydrator shown in Fig. 4 shows a verticalsectional view taken on line H of Fig. 3;

Fig. 5 is a front elevational view of one of the trucks bearing a plurality of superposed trays to be employed in connection with the apparatus illustrated in Figs. 1 to 3; and

Fig. 6 is a sectional detail view, somewhat fragmentary in character and at an enlarged scale, of the adjustable slots for the selective control of the drying gases over the individual trays.

Broadly stated, according to the principles of the invention, a drying chamber is provided within which the materials to be dried such as vegetables, fruits, and the like, are spread on a plurality of superposed trays for drying and within which a circulation of heated air is maintained. The upper portion of the chamber has the air-circulating means or fans mounted therein-while the lower part of the chamber is divided into three parts, the middle one of which contains the stack of superposed drying trays. To one side of these stacks of trays is a plenum chamber which communicates with the outlet of the fans. 0n the other side of the stack is pro vided an exhaust chamber having an exhaust duct to the atmosphere and having a vertical passage for the recirculation of air to the intake of the fans. The flow of the moisture-laden air from the exhaust chamber to the exhaust duct and to the vertical passage is controlled by means of dampers. If the air in the exhaust chamber does not contain too much moisture,

Suitable heating means such as steam heating pipes or coils, electric heating elements, gas or oil heaters, and the like, are provided for raising the temperature of the recirculated air. After the air passes through these heating means and is heated to the desired temperature, the fans suck the heated air in through inlet ports and then deliver it under pressure through the outlet ports to the plenum chamber and'to the stack of superposed trays. If the air which is being recirculated does not contain sufiicie'nt humidity then moisture may be added, for example, by means of an open steam pipe, or of a pet cock." Forguiding the air from the outlet of the fan to the stack of trays, a plurality of deflectors may be positioned in the plenum chamber although in some cases these deflectorsmay be omitted. A plurality of dampers mounted at the upper part of the deflectors may be used to controLthe amount of air passing between each pair of deflectors and in this manner control the amount of air going to the various sets of trays. For controlling the temperature and humidity within the drying chamber, a humidity and temperature control device is used capable of opening and closing dampers regulating the circulation of air through the dehydrating chamber and controlling the operation of the heating and humidifying means, as it will be described more fully hereinafter.

The essence of the process of the invention resides in subjecting the materials to be dehydrated to a plurality of cycles of treatments durin which the temperature, the humidity and the velocity of the drying gases, e. g., hot air, is maintained within critically adjusted limits. In-carrying the dehydration process of the invention into practice, the vegetables or fruits to be dried are peeled and pared and then are sliced, or shredded. The thus prepared vegetable or fruit is spread on perforated 0r screened trays, preferably made of aluminum. These trays are superimposed upon each other on a truck which is wheeled into the drying zone of the drying chamber. At the start, the air has a relatively lowheat and a relatively high humidity. Slow circulation of air under these conditions is continued .for a short period. Following the initial operation, the air under circulation is adjusted to a high heat and high humidity for a long period and the speed of cirthe vegetable or fruit has been dried, it is re-' moved from the drying chamber and then placed in a storage chamber which is maintained at a desired temperature and humidity or maybe .packed in appropriate containers under suitable conditions. Y

The invention will now be more, fully described in conjunction with the accompanying drawings. Referring now more particularly to Figs. 1 t 4 of the drawings, a preferred embodiment of the principles. of the invention into a dehydration machine is illustrated. The dehydration machine essentially comprises a casing I constituted of a metal frame 2 forming a support for a plurality of panels 2a. For compactness, the chamber is' practically cubicle-shaped with the exception 01' one side of the upper portion, which is sloped.

then it may be recirculated in whole or in part, Circulation of the gases within drying chamber I is obtalned'by means of two fans 3 which may be jointly actuated by means of a common shaft 4, having a pulley 5 mounted on one end thereof driven by an electromotor 6 by means of awith and is directly connected to the outlet of the fans. For guiding the air from the outlet of the fans to the stack of trays, a plurality of deflectors l5 are positioned in the plenum chamber which convert the substantially vertical flow of drying air into a horizontal flow. A plurality of dampers iii are adjustably mounted at the upper terminal portions of deflectors l5 and may be used to control the amount of air passing between each pair of deflectors and in this manner control the amount of air going to the various sets or trays.

It has been found that accurate control of the amount of air going to the various trays is of critical importance. This amount may be to some extent adjusted by setting dampers l8 into such positions that all of the trays, includin the highest and the lowest one, receive the preferred and desirable amount of air, in order to obtain uniform dehydration on all of the trays. In addition to this possibility of adjustment, a further adjustment is provided by incorporating adjustable slots l1 before the trays between the plenum chamber and the center chamber. will be best observed from Fig. 6 of the drawings, these adjustable slots are provided by mounting a plurality of pairs of L-shaped plates in horizontal and parallel-spaced position between the center and plenum chambers and in front of the stack of trays in the center chamber. One of each pair of such plates 18 is rigidly connected to the vertical rails forming part of the machine frame by means of welding or riveting. The other one of each pair'of such plates I8 is mounted in an inverted position and has an elongated slot at each end thereof so that it can be adjusted to any desired position and may be fixed in such As it position by means of a wing-nut 20. Thus, each pair of L-shaped plates defines a slot with the adjoining pair of plates, each of said slots being individually and accurately adjustable and is adapted to be fixed at a predetermined width. From the foregoing considerations, it is apparent that while dampers l6 at the upper portion of deflector plates l5 permit close adjustment of the amount of drying air passed to the various trays, the provision of the adjustable slots be fore the individual trays makes it possible to separately adjust the drying air for each individual tray whereby a control of heretofore unattainable accuracy is provided. Experiments have demonstrated that the extreme accuracy of this adjustment is one of the critically important factors in the production of a dehydrated product of high and uniform quality.

To the left side of the stack of trays is provided an exhaust chamber 2| having an exhaust duct 22 which is preferably connected to the external atmosphere outside of the building in which the dehydrating machine is located. Above exhaust chamber 2| is an intake chamber 23 which is in communication with both the upper portion of the exhaust chamber and with the intake side of the fan through a channel 24. In addition to this, the intake chamber is also provided with an opening or port 25 through which air maybe admitted from the proximity of the machine into the circulatory flow within the n achine.

The circulatory flow within the various chambers of the dehydrating machine is controlled by means of three dampers of which damper 28 is mounted in the external wall of exhaust chamber 2| and controls the discharge of air from the machine into the exterior atmosphere, damper 21 is mounted into the external wall of the intake chamber and controls the admission of air within the building into the machine, and damper 28 is'mounted in channel 24 between exhaust chamber 2| and intake chamber 23 and controls the circulatory flow within the machine. Each of these dampers comprises a plurality of plvotally mounted plates or vanes which are connected for joint operation by means of a lever mechanism and may be jointly displaced by means of suitable actuating elements. In dampers 28 and 21 these actuating elements include a small electric motor 38 which displaces the vanes by means of a lever rod 3|. The operation of damper motors 30 is controlled by means of a wet bulb thermometer or a similar humidity-responsive device 32, as those skilled in the art will readily understand. It will be noted that dampers 28 and 21 are simultaneously and synchronously actuated by their respective motors and that they are both in the open or closed position at the same time. ,On the other hand, the third damper 28 regulating the flow of air between the exhaust chamber and the intake chamber is connected to damper 21 by 'means of a lever rod 29 for to be automatically actuated in the opposite direction so that when for example damper 21 is open, damper 28 is closed, and vice versa.

Between the intake side of fans 3 and intake chamber 23 are provided heating means in the formof two banks of steam heating pipes or coils 33. Of course, instead of steam, heating with electricity, gas or oil may be employed, if preferred. Valve means are associated with these steam heating pipes to control the temperature within the chamber and to provide adjustable reheating of the recirculated air. These valve means are controlled by suitable thermostatic means such as a dry bulb thermometer 35 located at the outlet side of the fans. is being recirculated does not contain suflicient humidity, then moisture may be added by means of an open steam pipe, or petcock," 38 and an associated water tank 31 which are located between second heater 34 and fans 3. Wet bulb thermometer 32 and dry bulb thermometer 35 are connected by means of lead wires 44 to acontrol device or box whichis electrically associated with motors 38 of the dampers and with the valve actuating means of steam heating pipes 33 (not shown), to control the humidity and temperature conditions within the dehydrating chamber. In view of the fact that this control system is of conventional character, those skilled in the art are familiar with its operation. A screen 38 is provided between intake chamber 23 and the intake side of the fans to catch impuri- If the air which prevent sticking of the apples to the wire.

The construction of the truck bearing the trays on which the materials to be dehydrated are introduced into the' dehydrating chamber will be best understood from Fig. 5. The truck comprises a frame it constituted of iron'rails resting on wheels ii. A plurality of angle irons dd are mounted in the horizontal position at the two sides of the truck frame and are adapted to sup port trays 9. The trays comprise a wooden or.

metal frame covered with a wire mesh of suitable coarseness to facilitate passage of the gases therethrough. It has beeniound that the best material for making the wire mesh is aluminum, as aluminum is not attacked by the various acids contained in the materials to be dehydrated and does not impart any taste to the materials treated. In some cases, such as when dehydrating apples, it is advantageous to coat the wire mesh of the trays with high melting point paramn alone or containing a high melting point wax, etc., to

Between the various trays baille sheets M are provided which extend from the bottom of an upper shelf to the top of a lower shelf. These baiile sheets form a channel through which the circulated air can pass. These bafile sheets likewise are able to catch any condensate from the tray on an upper shelf and to carry such condensate, leakage, etc. to the side of the truck, thus preventing such condensate or leakage from dropping upon the vegetable, fruit, etc. to be dehydrated on the tray below. The trays are so spaced on the truck that the streams of dehydrating air defined by adjustable slots ll of the plenum chamber will be directly introduced into the space between the trays and are caused to pass through the materials on the trays.

From the foregoing description, the operation of the dehydrating machine embodying the invention will be readily understood by those skilled in the art. The vegetable or fruit is first prepared by peeling, paring, slicing, shredding, etc., or subjected to other operations of similar character, if necessary, and is spread on the perforated or screen trays which are stacked in superposed relation on the trucks. In the preferred embodiment of the invention described and illustrated, two of such trucks are rolled into the rying chamber and doors 42 at the two ends of (1 ng chamber 8 are closed to seal the chamber. As has been explained in the foregoing, to the one side of the trucks adjacent to the plenum chamber, a panel is provided with a series of superposed adjustable slots H, which are located in alignment with the space between the trays. These slots are adjusted and are locked in this adjusted position, in accordance with the character of the materials to be dehydrated so that the proper amount of air can be admitted to each of the trays. In general it is desired to have a uniform stream of air passing through the slots at approximately the same velocity, thereby delivering approximately the same amount of air to each tray. 7 Depending upon the fruit, vegetable or other material to be dried, the index arms of the dual controller controlling the humidity and the temperature within the dehydrating chamber are set to the dry bulb and wet bulb thermometer readings corresponding to the desired conditions of temperature and humidity within the drying chamber. The two fans 3 are then started in operation by energizing electromotor 6. The air will .be circulated at the temperature and the humidity set by the index arms. Usually, at the start of the operations, the wet bulb thermometer is too low and therefore the wet bulb thermometer acts through its thermal system to open the heater spray from the open steam pipe 36 and to close the fresh air and exhaust dampers 2i and 26, respectively, while opening the recirculation damper 28. The dry bulb thermometer likewise acts through its thermal system to open the provided damper 28 is open.

steam valves controlling the steam to heaters 33. In this manner, the temperature and humidity of the air being recirculated is adjusted to the desired temperature and humidity, and a closed circulatory flow is maintained within the drying chamber.

During the recirculation of the air, the stream of air emerging from fans 3 passes over dry bulb thermometer 35 and wet bulb thermometer 32 and then into plenum chamber i i. In the plenum chamber, the stream of air is divided into a plurality of individual streams by means of deflectors l5 and are guided to the plurality of superposed adjustable slots I! and pass into the spaces underneath each tray 9. Inclined baflies 4! between each pair of adjoining trays cause the air to flow upward through the material on each perforated tray into the space above the tray and then out into exhaust chamber 2|. From the exhaust chamber, the air flows partially or wholly to exhaust duct 22 in case damper 28 is closed or to thevertical passage communicating with intake chamber 23, Fresh air may be admixed with the recirculated air. It is to be noted that this fresh air comes from the room in which the drying chamber is located and is not taken from outdoors.

When the recirculated air passes through th material on the tray, its temperature falls and its humidity increases. The dual controller automatically adjusts the steam valve and the various dampers to control the temperature and the humidity of the air. In this manner, the recirculated air which is delivered to the trays is maintained practically constant with respect to temperature and humidity. It is to be noted that the minimum humidity of the system is limited by the moisture content of the fresh air and that the maximum temperature is limited by theheating capacity of heaters 33, the steam pressure, the percentage of cold fresh air admitted through damper 21 for securing the desired humidity, and various other factors which are readily appreciated by those skilled in the art.

, In carrying the dehydration process embodying the presentinvention into practice, the oper ating conditions .are so adjusted that at the start the air has a low heat and a high humidity. Slow circulation of air under these conditions is continued for a predetermined andrelatively short period of time. Following this initial operation, the air under circulation is adjusted to a high heat and high humidity for a relatively long period, and at the same time the speed of circulation is increased. To complete the drying. the air is then circulated at a reduced heat and reduced humidity. This reduced heat and humidity can be adjusted until the final temperature and final humidity have been reached. Thus, the drying period may" end with air being circulated at medium heat and low humidity. When the vegetable or fruit has been dried, it is removed fromthe drying chamber and is placed into a storage chamber which is maintained at the desired temperature and humidity, or which may be packed in appropriate containers under suitable conditions.

Generally speaking, the preferred operations,

included in the dehydration process embodyingthe present invention may be listed as follows: 1. Peeling and paring the vegetables or fruit. 2. Slicing, cubing and shredding. 3. Spreading on perforated or screen trays.

4. superimposing the trays in the drying chamber.

5. Recirculating a current of air at low heat (sayat about 150-160 F.) and high humidity- (say about 20-35%) pulled at same rapid velocity I for about an hour. This step may sometimes be eliminated, in the discretion of the operator, depending upon the fruit or vegetable being dried and' upon particular conditionsand circumstances.

8. Recirculating a. current of air at medium heat (say at about 140-170 F.) and low humidity (say about 15-20%) pulled at the same high velocity until the vegetables or fruit are dried.

9. Removing the desiccated food product.

The preferred drying operation may be divided up into an initial or short period, an intermediate or long period, a supplementary or medium period, and a. final period. In some instances, the

supplementary or medium period may be eliminated. These periodsmay be illustrated by the following fiow sheet:

Initial or short period Slow fan Low heat (150-160 F.) High humidity 65-50%) Less than 1 hour v Intermediate or long period Full fan Medium heat (150-170 F.)

Reduced humidity (15-30%)' Time to suit Final period Full fan Medium heat (mp-17o" F.)

Low humidity (5-1 5%) Balance of drying time For the purpose of giving thoseskilled in the art a better understanding of the invention, the following illustrative examples may be given:

. Example No. 1.

About 1000 pounds of cherries are washed and after 'removal of the stones and stems are spread on the trays of the trucks wheeled into the drying chamber. The initial treating periodutilizes a starting temperature of about 150 a relative humidity of about 30% and a slow fan for about one-half hour for .the initial or short period. During the intermediate treatment, the temperahumidity of about 30% is maintained with a full fan for about 2 hours. dium period is used and a temperature of about 170 F. and a relative humidity of about 20% is employed with a full fan for about 1 hour. During the final period, a temperature of about 170 F. and a relative humidity of about is maintained with a full fan for the balance of the drybe packed as desired.

' I Example No. 2

sliced and are then spread on the trays introduced into the dehydrating chamber. An initial treating period is used with a temperature of about 160 F. and a relative humidity 01' about with a slow fan for about one-quarter hour. 30 The intermediate period then follows with a temperature of about 190 Rand a relative humidity of about 25% with a full fan for about 2 DOUiS. The supplementary or medium period is omitted, and during the final period a temperature or about 185 F. and a relative humidity of about 10% ismaintained with a full fanior the balance of the drying time. u

Example N0. 3

About 1000 pounds of potatoes are pared and sliced and are then spreadon the trays introduced into the dehydrating chamber. An initial treating period is used with a temperature oi about 150 F. and a relative humidity of about with a slow fan for about 15' minutes, this being followed by a second initial treating period with a temperature of about; 165 F. and a relative humidity of about 35% with a slow fan for another 15 minutes. The intermediate period then follows with a temperature of about 160 F.

and a relative humidity of about 30% with a midity of about 25% is maintained .with a full fan for the balance of the drying time.

In the event that it is desired to blanch vegetables or fruits, blanching steam-may be directly admitted to the trays on the truck within the drying chamber. Likewise, in some cases it is desirable to treat the vegetables or fruits with sulphur dioxide fumes or other vapors or gases for a suitable period of time. For thi 'purpose it is preferred to make provision for shutting oif the drying chamber proper from the fans and from the motor as the heavy steam used in blanching is injurious to the Ian bearings and the sulphur dioxide fumes are likely to strongly attack the motor fittings with In this manner, it is possible ture is raised -to about 190 F., and a relative.

A supplementary or meing time. After the final period, the dehydrated cherries may be kept me. storage chamber or may About 1000 pounds of apples are pared and disastrous results. to carry out these supplementary treatments within the drying ap- 1 that may be given to potato or cabbage.

tional handling may be eliminated.

The product produced by the process embodying the present invention isunique in character and has properties vastly superior to those of conventional dehydrated products. While prior art dehydrated products are usually powdery, flaccid, leathery, colorless and lacking flavor, the products prepared in accordance with the principles of the invention, can be soaked in waterand they will return approximately to their natural size and color and possess the natural flavor and wholesomeness of the original product. We have found that in conventional drying and dehydrating processes, the cell membranes of the materials become case-hardened through the necessarily high drying temperatures, causing the internal water to expand and to burst open the cell walls whereby the volatiles arelost and air entering the ruptured cells causes oxidation and destruction of the vitamins, chlorophyll and other substances upon which the nutritive value of fruits or vegetables depends. In contrast to this, the carefully controlled sequence of the treating steps of the invention involving the maintenance of critical temperature, humidity and gas velocity conditions for predetermined periods of time, completely eliminates these disadvantages of prior dehydrated materials and permits the production of dehydrated materials having all of the desirable properties of the original materials. a

We believe that these remarkable and unique properties of the dehydrated products prepared in accordance with the principles of our invention are dueto the fact that we carefully maintain our treating conditions, including temperatures, below a critical limit which, for convenience, may be called the thermal death point of the materials to be dehydrated. We found that when this critical limit is surpassed, case-hardening occurs with the consequent, deterioration and destruction of the cellular structure characteristic of conventional dehydrated products. If the cells are broken open, air enphyll, carotene and other vitamins and vital principles. the material to be dehydrated, and what is a suitable maximum treating temperaturefor one material would be excessive and disastrous for another. For example, apple will stand 190 F. without any ill eifects while 160 F. is about all The fact that the treating temperatures of the process embodying the present invention are below the thermal death point of the various fruits and vegetables is proved by the observation that seeds dried by the process otthe invention will grow again in a suitable surrounding. Thus, for example, tomato seeds have grown for 4 or 5 generations after drying each generation by means of the apparatus and method embodying the mvention.

Microscopic examination of. the cellular structure of the products of the invention shows that in the products embodying the present invention,

' tering the ruptured cells destroys the chloro-' Of course, this critical limit varies with the cellular structure remains substantially inlular-structure of our dehydrated products and "paratus and the cost and delay caused by additheir freedom from cracks, splits, etc., is respon-' sible for their remarkable properties outlined in the foregoing.

It will be noted that the present invention provides a number of important advantages. Thus, first of all, a novel and improved process for dehydrating foodstuifs is provided which preserves the cellular structure, appearance, taste, flavor, wholesomeness and vital principles of the original material to such an extent that the dried or dehydrated materials may be restored to substantially their original condition by restoring their original content of water.

It is also to be observed that the dehydrated products of the invention have in most cases less than about 15 or 20% of the. weight of the original product, require only a fraction of the space for storage and can be kept in storage for a number of years without deterioration. Thus, for example, one bushel of carrots in the dehydrated condition is reduced in volume to about /2 gallon and ten pounds of tomatoes are reduced in volume to about pint,

Moreover, the process of the invention is extremely simple in character and is capable of dehydrating large quantities of materials within an unprecedentedly short time and at a heretofore unattainable low cost on a practical and industrial scale. Thus, inaddition to apples, cherries and potatoes, the process embodying the invention may advantageously be used for dehydrating various other foodstufis including fruits and vegetables. For example, spinach, beets, parsely may be dehydrated in three treating periods involving treating temperatures of 150 to 160 F., 160 to 175 F. and 145 to 175 F., respectively and humidities of 25% to 35%, 25% to 35%, 15% to 20%, respectively. Blueberries, peaches, carrots, peppers, string beans, cabbage, celery, wax beans and tomatoes may be dehydrated in four treating periods involving treating temperatures of to 160 F., 160 to 185 F.. 150 to 185 F. and to 175 F., respectively,

and humidities of 25% to 45%, 25% to 45%, 15%

to 40% and 15% to 30%, respectively. Turnips, onions and peas maybe dehydrated in five treating periods involving treating temperatures of to F.,'160 to F., 160 to 180 F., 150. to 170 F., and 145 to 170 F., respectively, and humidities of 35% to 40%, 30% to 40%,

25% to 35%, 20% to 25% and 10% to 15%. re-

be resorted to by those skilled in the art without departing from the principles of the present invention. We consider all of these variations and modifications as within the true spirit and scope of the present invention as disclosed in the'foregoing description and defined by the appended claims.

We claim:

1. The process of dehydrating foodstuffs which comprisesestablishing a circulatory flow of air within a=closed space and in contact with the foodstuiis to be dehydrated, maintaining said.

flow at a temperature of about 140 to about 160 F. and at a humidity of about 25% to about 50% for a first treating period of the order of about one-quarter hour toabout one hour, maintaining said flow at a temperature of about 160 to about F. and at a humidity of about 25% to'about 50% for a second treating period of the order of about one-half hour to several hours and longer than said first treating period, and subsequently maintaining said flow at a temperature of about 140 to about 170 F. and at a humidity of about to about 30% for the balance of the drying time whereby a dehydrated product free from case-hardening eiiects and retaining the original cellular structure is obtained, said dehydrated product being adapted to be substantially restored by the addition of water to a product having the appearance, size, texture and flavor of the fresh foodstuffs.

2. The process of dehydrating foodstuffs which comprises establishing a circulatory flow of air within a confined space and in contact with the foodstuffs to be dehydrated, maintaining said flow at a temperature of about 140 to about 160 F. and at a humidity of about 25% to about 50% the order of about one-quarter hour to about one hour, maintaining said flow at a temperature of about-160 to about 190 F. and at a humidity of about 25% to about 50% for an intermediate treating period of the order of about one-half hour to several hours and longer than said initial treating period, maintaining said flow at a temperature'of about 150 to about 170 F. and at a humidity of about 15% to about 30% for a supplementary period of the order of about one-half to about one hour, and subsequently maintaining said flow at a temperature of about 170 to about 190 F. and at a humidity of about 5% to about 30% until said pletely dehydrated and" a dehydrated foodstuff free from case-hardening efiects and retaining the cellular structure of the original foodstuffs is obtained, said dehydrated foodstuff .being adapted to be substantially restored by the addition of water to a product having the appearance, size, texture and flavor of the fresh food- 3. The process of dehydrating foodstuffs which comprises establishing a circulatory flow of airwithin a confined space and in contact with the foodstuffs to be dehydrated, maintaining said flow at a temperature of about 150 to about 160 for an initial treating period or foodstuffs are comfor a period of the temperature of about 180 order of one-half to heat to about 170 F.

ty of about 30% to about 45% order of about one-quarter maintaining said flow .at a to about 190 F. and at a humidity of about 30% to about 40% for a period or the order or about one-half to about two hours, and subsequently flow at a temperature or about F. and at a humidity of about 15% until said foodstufls are completely and a dehydrated foodstuff ening eflects and retaining 'the cellular structure of the original roodstufls is obtained, said dehydrated roodstufl being adapted to.be substantially restored by the addition of water to a product having the appearance, size, texture and flavor of the fresh foodst 4. The process or dehydrating foodstufls which comprises establishing a circulatory flow of air F. and at a humid to about one hour,

to about to about 20% dehydrated within a confined space and in contact with the v foodstuffs to be dehydrated, maintaining said flow at a. temperature of about 150 to about 160 F. and at a humidity of about 30% to about 45% for a period of about one-quarter to about one hour, maintaining said flow at a temperature of about to about F. and. at a humidity of about 30% to about 40% a few hours, reducing said and said humidity to about 20% to about 35% for a supplementary treating period of the order of about one-half to about one hour, and subsequently adjusting said temperature to about 160 to about 170 F. and said -humidity to about 15% to about 20% until said foodstuffs are completely dehydrated and a dehydrated foodstuff free from case-hardening effects and retaining the cellular structure of the original foodstufis is obtained, said foodstufl being adapted to be substantially restored by the addition of water to a product having the appearance, size, texture and flavor of the fresh foodstuffs.

GEORGE A. SYKES.. AGNES LOUISE ANDREA.

-maintaining said.

tree from case-hardfor a period of the 

